1. Field of the Invention
The present invention generally relates to cleaning devices for mechanically cleaning surfaces and, in particular, to devices for cleaning the ferrule end surface of an optical fiber which is installed in a ferrule connector such as a plug or a bulkhead for interconnection with another optical fiber or with an optoelectronic device.
In fiber optic networks, optical fiber strands, which typically have a diameter of about 8 micrometers, are connected by encasing the strands in protective jackets to form cables and butting two cable ends together. To do this, the ends of the individual fiber optic strands 10a, 10b, 10c (FIGS. 1A, 1B, 1C) are typically stripped of the jacket and are bonded and encased in the center of a rod-like ceramic ferrule 12a, 12b, 12c. This ferrule provides an enlarged surface area for finished polishing of the exposed end face of the optical fiber strand. The ferrules generally conform to standard sizes having end faces with diameters of 1.25 millimeters (mm), 1.6 mm, 2.0 mm or 2.5 mm. The ferrule end faces 14a, 14b, 14c (and the unnumbered end faces of the optical fibers therein) are polished either flat (FIG. 1A), slightly convex (FIG. 1B), or angled at approximately 8 degrees (FIG. 1C) to reduce reflected light when connected to another optical fiber. These ferrules are then fitted into variations of connector housings, e.g., connector 18 (FIG. 2), which precisely interconnect with similar devices, e.g., connector 18′ (FIG. 3), via a coupler or bulkhead 20 to insure the exact alignment of the butted optical fiber strands. Cleanliness of cable connections is a critical factor in maintaining peak signal communication performance.
In spite of all the above preparations, these connections are highly susceptible to contamination at the abutting end faces of the optical fibers. Specifically, the optical transmission capability of the junction between the optical fibers can be significantly impaired by microscopically small deposits of contamination on the end surfaces of the fibers. Sources of such contamination include smoke, dust, dirt, moisture and other ambient contaminates; oils, salts and particles transferred from the skin of technicians during connector manufacture and assembly, cable installation, or job site service work. Small amounts of contamination in the form of particles or haze will significantly increase light attenuation across the butted connection. Therefore, it is essential that the end surfaces be cleaned before the optical fiber ends are connected to each other, and/or after they become contaminated during normal use.
2. Related Art
Prior art practice in the maintenance of optical fiber connectors is to rub the ferrule end against a fabric- or paper-based cleaning strip. This method requires that the ferrule end be fully exposed for proper cleaning, but this is often impractical because the ferrule end is often recessed within a connector or coupler and it would be necessary to disassemble the connector or coupler in order to clean the ferrule end. In these circumstances, the ferrule end is sometimes cleaned using a swab made of soft absorbent material(s) such as paper, fabric, foam or combinations of the three that is inserted into the connector or coupler and rotated along its axis to clean the ferrule end. Both the fabric strips and the swabs are often saturated in isopropyl alcohol as a cleaning solvent to assist the process. This method is flawed because swabs, by design, typically provide the best cleaning surfaces only along the outside diameter of the swab, i.e., on its sides, and not on the end. Thus, when inserted in the connector, coupler or bulkhead, the best cleaning performance will be along connector sidewalls, not where needed on the ferrule ends. In addition, adhesive and/or thermal bonding methods used to assemble the swab will often include or produce volatile compounds that are diffused during use and which contribute to the microscopic contamination of the ferrule end surface.
The contamination introduced by a prior art swab can be exacerbated when a cleaning solvent is used with the swab, because the solvent may dissolve and/or accelerate the physical decomposition of the bonding adhesives, urethane foams and other materials used to manufacture the swab. Finally, many prior art swabs use loose-stranded fibrous materials such as non-woven cotton or spunlaced polyester fabrics. These loose, non-woven strands tend to shed numerous particles that are larger than the 8-micrometer diameter of the fiber optic strand. The result is inadequate or incomplete cleaning of the ferrule end connection.
Thus, prior art cleaning methods and devices provide uneven cleaning performance.